Patent Document 1 discloses one example of a rechargeable battery device that serves as a battery pack including battery modules. The rechargeable battery device described in Patent Document 1 includes assemblies of stacked batteries. Each assembly of stacked batteries includes a floor plate, a back plate projecting from the floor plate, and a base plate fixed to the floor plate. A battery module is mounted on the base plate. The battery module contacts the back plate. Side plates, which project from the edges of the base plate, sandwich the battery module. A packing is arranged on the battery module, and another base plate is arranged on the packing. Another battery module is mounted on the base plate. In this manner, the battery modules are stacked.